This is a continuation of services to other investigators to provide pregnancies of known gestational ages and to monitor fetal growth in rhesus monkeys (Macaca mulatta). The monkeys' cycles are controlled by the daily injection of progesterone (5 mg/day) for 10 days. Females are paired with males on days 14 to 21 after the last progesterone injection. Ovulation and conception occurs on day 16 to 18 after the progesterone injections. Success rate, based on viable fetus at 21 days gestation, remains at 60% to 70% for first cycle matings. Fetal development is monitored by weekly ultrasound exams until time of parturition. At each exams measurements at taken, depending on gestational age, to determine gestational sac length, crown-rump length, heart rate, femur length, and bipartial diameter. Evalualtion of the placental disks are made to determine any anomalies. These procedures provide investigators with the ability to conduct studies at specific stages of gestation and to determine any effects on the fetuses.